What to Know About an Infused Knee

Medically Reviewed by Dan Brennan, MD on June 29, 2021

If your knee is swollen, it's also called an infused knee. Swelling happens when fluid builds up around or behind the joint in your knee. An infused knee may also be called an effusion in your knee joint or “water on the knee”.

Understanding an Infused Knee

If you have knee pain or an injury to your knee, swelling may be a factor. Swelling is usually obvious because of the change in your knee’s appearance. But other signs of knee swelling include discomfort, pain, or loss in your range of motion. ‌

Knee swelling is often the result of:

  • Traumatic injuries like fractures and meniscus or ligament tears
  • Infections in your knee, which are rare but can be severe‌
  • Overuse of the joint from repetitive movements ‌

Of all causes, overuse is the most common reason for an infused knee. Fluid buildup is your body’s way of protecting the area from extra damage. You may have minor swelling after a vigorous activity. This can also be an early sign of arthritis. If you have persistent swelling, talk to your doctor about your concerns.

An infused knee can happen at the front of your knee, called an anterior injury. It can also happen at the back of your knee, called a posterior injury. Anterior swelling is much more common than posterior because of the way we use our knees for activities.

Symptoms of an Infused Knee

Swelling, stiffness, and pain are the main signs of an infused knee. Your pain or discomfort will vary based on the severity of your injury and any other health conditions you may have. Fluid buildup can limit your range of motion, making your knee feel stiff even if there isn’t pain.‌‌

Your injury may be so severe that you can't move your knee at all. Always talk to your doctor about your concerns if you injure your knee, even if you don’t have symptoms.

Complications of an Infused Knee

An infused knee can lead to other health concerns if left untreated. This includes loss of muscle in the affected leg. Persistent swelling may leave you using your knee less and losing muscle mass in that leg. Or you may develop a Baker's cyst, which is a sac filled with fluid that forms behind your knee.‌

Diseases or health conditions that may make your swelling worse include: 

  • Bursitis
  • Cysts
  • Gout
  • Infection
  • Osteoarthritis
  • Rheumatoid arthritis‌
  • Tumors

Diagnosing an Infused Knee

Your doctor will ask you about any past injuries. If you’re not sure when the swelling began or what caused it, your doctor will consider your age and activity level. If you do sports regularly, that may be a factor. If you’re overweight or obese, extra weight may add stress to your knee joint and increase the swelling.

Treating an Infused Knee

Home treatment. You can try treating an infused knee on your own by following the RICE protocol, which stands for rest, ice, compression, and elevation. You can also take over-the-counter anti-inflammatory medication.‌‌

Rest is important in allowing your knee the chance to heal so swelling goes away. You may be tempted to work through the swelling, especially if you don’t have any pain or discomfort. But swelling is a sign that something is wrong, and it’s important to pay attention to your body. ‌

Medical Treatment. If treating your infused knee at home isn’t enough, talk to your doctor. Seek treatment if your knee is red or warm to the touch. This may be a sign of infection.‌

In the case of an infection, your doctor may want to remove some of the fluid to reduce irritation to your knee joint. Removing the fluid can ease stiffness and improve your range of movement so you can begin to build muscle mass in your leg again.‌

Removing some of the fluid helps reduce the pain and stiffness linked to the swelling. Your doctor might do more tests to determine if an underlying health condition is a factor. If so, treating that condition may ease your infused knee symptoms.

Preventing an Infused Knee

Tips for preventing a knee injury include:

  • Incorporate strength exercises into your routine. Strong muscles supporting your knee joint can help prevent injuries.
  • Prioritize lower-impact exercises. By eliminating stress to your knees, you can decrease your chances of an infused knee‌.
  • Watch your weight. The heavier you are, the more pressure is on your knees, making any injuries worse. 

Show Sources


Journal of the American Family Physician: “Acute Knee Effusions: A Systematic Approach to Diagnosis.”

Mayo Clinic: “Swollen Knee.”

Sutter Health: “Swelling Behind Knee.”

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